Tried using anti-seize on spark plug threads for the first time and it totally backfired

Last month I put a light coat of copper anti-seize on the spark plugs of a Lycoming engine. Thought I was being smart preventing galling. Well, two of them backed out after 15 flight hours and I had to pull the cylinder to fix the stripped threads. Learned that torque values change with lubricants, so now I just install them dry per the manual. Has anyone else had a similar experience with anti-seize on aero engines?

2 comments

2 Comments

alice_reed4714d ago

Man, you are not alone on this one. I did the exact same thing on a Continental O-470 a couple years back. Thought I was being clever and put a thin layer of anti-seize on the plugs like I do on my car. Three flights later and one plug was barely finger tight, felt like it was about to fall out. Scared me half to death. The manual says dry torque for a reason, and I learned that lesson the hard way too. The torque wrench reading is totally different when you add lubes, it throws everything off. Now I just run them in clean and dry like the book says, and check the torque after the first couple of hours. Saved my engine from a major headache.

black.margaret13d ago

I actually heard a pretty wild story from a guy at my local EAA chapter about this. He did the same thing with anti-seize on his Lycoming, and when he went to check torque after five hours, three plugs spun out by hand. He said the g-forces from just normal flight maneuvers were enough to back them out. Now he swears by the rule of thumb I read somewhere: if your engine manual says dry torque, that means totally dry, not even a wipe of oil on the threads. It's scary how such a small change can turn a routine spark plug change into a potential engine failure.